Electric primer



` Jan. 3, 1967 HANS-DIETER HARNAU 3,295,446

ELECTRIC PRIMER Filed Mar'Ch 5, 1965 .nited States atent 3,295,446 ELECTRIC PRIMER Hans-Dieter Harnau, Gevelsberg, Westphalia, Germany, assigner to Firma Rheinmetall G.m.h.H., Dusseldorf, Germany Filed Mar. 5, 1965, Ser. No. 437,520

Claims priority, application Germany, Mar. 12, 1964,

6 Claims. (Cl. 102-28) This invention relates to an electric primer of the type having an electric priming element consisting of a central electrode mounted within a cylindrical outer electrode whose rim is bent towards the centre electrode and terminates in at least one contact point. There is an insulating element between these two electrodes which is coated on its surface between the central electrode and the contact points with a thin homogeneous metal film connecting the electrodes. This metal lm is in contact with the contact points and the central electrode. The `action of the priming element is based on the knowledge that, in operation, at lthe point of contact between the surface of a thin homogeneous metal iilm connected to one terminal of a current source used to actuate the priming element and a conductive point connected to the other terminal of` the current source, the metal lm fuses owing to the high current density. The melting process takes place very rapidly, and appears -as a mere spark. This phenomenon is exploited in the case of a conventional priming element. It offers the advantage that the priming composition is arranged to be in contact with the sparkproducing area, and this is a basic condition for proper ignition. Moreover, the number of individual components in the above-mentioned known priming element is low, and these components are of simple construction.

.The present invention has for its object to provide a suitable detonator for a priming element of the type just described which when tted to a primer, suitable, for example, for fitting in cartridge cases, constitutes an improvement in comparison with -conventional electric primers.

A further known concept on which this invention is based is that the outer electrode of a wound or spiral capacitor at whose end face a multiplicity of spark gaps is formed, can be arranged in a metallic retaining ring which also functions yas the outer terminal, and that the inner electrode of the capacitor can be slipped over a metallic core constituting the inner terminal. The retaining ring rests on the core, an insulating washer being interposed, so that the wound capacit-or, the retaining ring, the core and the insulating washer form a unit capable of being installed in a primer. According to prior art, this installation vis accomplished by caulking.

The task which the present invention is to solve is the installation in a primer of a priming element, known per se, by means of a support arrangement Whose several constructional components have already been disclosed in connection with a priming element basically operating in a different way. This object is achieved by arranging the outer electrode in a metallic retaining ring which is held in a stepped bore in the primer body in such a way that it presses an insulating washer against an anvil, the inner electrode projecting through the insulating washer being electrically connected to the anvil.

A primer constructed in this way offers the advantage that the insulating washer cannot be compressed beyond a required degree, and the priming element cannot be shifted from its axial position by a jammed retaining ring,

,so as to render the insulating effect of 4the washer un- ICC A threaded electric primer embodying the invention will now be described in greater detail with reference to the accompanying drawing which is a cross-section of the primer.

The primer comprises a cylindrical metal body 1, preferably of brass, which is externally screw-threaded as at 2, a stop flange 3, and a key-receiving extension 4. By means of a key (not shown), which engages the key extension 4, the threaded primer can be screwed, for example into a cartridge case, up to its stop flange 3, lthe case being provided with a counter-thread matching the thread 2.

Internally, the metal body of a threaded primer has an open-ended axial bore with several internal shoulders. As seen in the drawing, the lowest shoulder supports a sleeve-like insulator 5 into which an anvil 6 of T-shape'd cross-section is forced. The anvil 6 has an open-ended axial bore whose diameter is prefer-ably smaller at the narrower portion of the anvil than it is in the wider p0rtion of the anvil. When the insulating sleeve 5 and the anvil 6 lhave been introduced int-o the lower part of the metal body 1, the lower opening of the bore of the threaded primer, which is tapered in the manner of a funnel, is closed. The insulating sleeve 5 projects internally beyond the anvil 6, so that it engages an insulating washer 8 which rests on the anvil. The insulating washer 8 as well as the insulating sleeve 5 consist of synthetic material, but the insulating washer may be of a ceramic material.

In the bore of Athe anvil 6, an inner electrode 9 of a priming element is held by a solder 7. The electrode 9 is hollow and is of steel. That end of the electrode 9 facing away from the anvil 6 is funnel-shaped. By devising the inner electrode in this way, it becomes possible to introduce the solder together with the anvil. The bore in the anvil allows air to escape downwardly during soldering. A further advantage of this electrode design is that the inner electrode is not normally in contact with the c-omparatively hard brass, but only the solder, thus being allowed to penetrate more deeply and to achieve better contact for initiating the ignition process.

Surrounding the inner electrode is -a ceramic insulator 10. The funnel-shaped upper portion of the inner electrode offers the advantage that adhesive friction between the inner electrode 9 and the surrounding ceramic insulator 10 is ensured.

Around the insulator 10 is an outer elect-rode 13 with a contact point 12 and those portions of the surface of the insulator 10 which are in contact with the contact point 12 of the outer electrode 13 .are coated with a metal film 11. The outer electrode 13 may have several contact points. The electrode 13 is forced into a metallic retaining ring 14 which rests on one of the internal shoulders of the bore in the metal body 1 ofthe threaded primer and is h eld in position by a -caulking 15. The design of the retaining -ring 14 and its mounting ensure that the insulating washer 8 cann-ot .be unduly compressed `and the priming element shifted from its axial position, due to jamming of the retaining rin-g. This could lead to the in'- sulating sleeve 5 becoming damaged, and undesirable contact being made when a voltage is applied, with a short-circuit .and the elimination of the priming element being the result. The bearing pressure exerted by the caulked retaining ring 14 upon the insulating washer 8 can be determined in advance by selecting the thickness of the latter. To increase the spark length between components yat diferent potential, the distance between the insulating washer 8 and the metal body 1 can be increased by increasing the inner diameter of the metal body at this point. In a device embodying the invention, even a narrow shoulder will give the retaining ring sucie'nt support.

Since the electric field is strongest at the edges and the risk of flash-over is therefore greatest at these points,

the anvil 6, as well as the portion of the metal body 1` in facial relationship therewith, is rounded at the edges by turning. This offers the additional advantage that the insualting sleeve 5 will not be damaged when the anvil 6 is introduced in the metal body 1.

The outer electrode 13 projects in the axial direction beyond the metallic retaining ring 14 and the inner elecltrode 9. In this way a hollow cylinder is formed above the insulator 11i-the cylinder being interrupted merely by the contact point 12--and a primer pellet 16 is located in this cylinder. When a spark is produced by fusing the metal coating 11, it is this primer pellet 16 which ignites first. Above the retaining ring 14 and the primer pellet 16 is a layer of loose black powder 17 which is followed, in the present embodiment, by a final layer of compressed black powder 18. In the latter there is provided a central opening, also filled with loose black powder. At this end, the threaded primer is closed by a disc 19 engaging a groove provided in the metal body 1. The sealing disc 19 is retained by a metal ring 20 engaging the same groove. The threaded primer of the invention is sealed off with shellac at this end.

The threaded primer described above is reliable in operation and is impact and acceleration proof, because it does not include any resilient contacts or connections, for example. The threaded primer is of simple construction and therefore suitable for cheap mass-production.

What I claim is:

1. A primer comprising in combination an electric priming element including a center electrode, a cylindrical outer electrode around said center electrode, a rim on said outer electrode bent towards said center electrode 'and terminating in at least one contact point, an insulator located between sai-d center yand outer electrodes and having a surface between said electrodes, a metallic coating on said surfa in connection with said electrodes, means for holding said primer element including a sleevelike body, said body having an open-ended axial bore therethrough and having a iirst end directed towards a mass to be primed by the primer and a second end opposite to said iirst end directed outwardly for electrical contacting purposes, an internal shoulder at said second end, a metallic retaining ring in said bore, said primer element being mounted in its entirety in said retaining ring by forcing in said outer electrode, an anvil located in said bore and residing on said shoulder, a thin insulating layer disposed between said shoulder and said anvil, an insulating washer disposed between said metallic retaining ring and said anvil, said retaining ring being pressed in a direction to said second end against said shoulder by means of said insulating washer, said anvil 'and said thin insulating layer, and said center electrode of said primer element projecting through said insulating washer and being connected electrically with said anvil.

2. A primer comprising in combination an electric priming element including a center electrode, a cylindrical outer electrode around said center electrode, a rim on said outer electrode bent towards said center electrode and terminating in at least one contact point, an insulator located Ibetween said center and outer electrodes and having a surface between said electrodes, a metallic coating on said surface in connection with said electrodes, means for holding said primer including a sleeve-like body, said body having an open-ended axial bore therethrough and having a lirst end directed towards a mass to be primed by the primer and a second end opposite to said iirst end directed outwardly for electrical contacting purposes, an internal shoulder at said second end, a metallic retaining ring in said bore, said primer element being mounted in its entirety in said retaining ring, an anlvil located in said bore and resting on said shoulder, a thin insulating layer disposed between said shoulder and said anvil, an insulating washer disposed between said metallic retaining ring and said anvil, said retaining ring being pressed in a direction to said second end against said shoulder by means of said insulating washer, said anvil and said thin insulating layer, said anvil extending outwardly through said second end `and having an openended axial passageway extending outwardly therewith, said center electrode of said primer element projecting through said insulating washer and being secured in said passageway by electrically connecting solder, and said solder extending through said entire axial passageway to be struck for electrical contacting purposes.

3. A primer comprising in combination an electric priming element including a center electrode, a cylindrical outer electrode around said center electrode, a rim on said outer electrode bent towards said center electrode and terminating in at least one contact point, an insulator located between said center and -outer electrodes and having a surface between said electrodes, a metallic coating on said surface in conection with said electrodes, means for holding said primer element including a sleeve-like body, said body having an open-ended axial bore therethrough and having a rst end directed towards a mass to be primed by the primer, a second end opposite to said first end directed outwardly for electrical contacting purposes, an intern-al shoulder at said second end, a metallic retaining ring in said bore, said primer element being mounted in its entirety in said retaining ring by forcing in said outer electrode, said outer electrode being a force t in said metallic retaining ring, an anvil located in said bore and resting on said shoulder, a thin insulating layer disposed between said shoulder and said anvil, an insulating washer disposed between said metallic retaining ring and said anvil, said retaining ring being pressed in the direction to said second end against said shoulder by means of said insulating washer, said anvil and said thin insulating layer and being held in said bore by caulking the inner wall of said bore in `a direction from said first to said second ends, and said center electrode of said primer element projecting through said insulating washer and being connected electrically with said anvil.

4. A primer with an electric priming element comprising, a center electrode, a cylindrical outer electrode around said center electrode and having thereon a rim bent towards said inner electrode and terminating in at least one contact point, an insulator located between said center and outer electrodes and having a surface between said electrodes, a metallic coating on said surface connected with said electrodes, said primer having -a shouldered -bore therein, a metallic retaining ring in said bore, said outer electrode having a force tit in said metallic retaining ring, caulkin-g holding said metallic retaining ring in said bore, an anvil provided in said bore and having an open-ended passageway therein, said center electrode being secured in said bore by solder, and an insulating washer disposed between said metallic retaining rring and said anvil, said center electrode projecting through said insulating washer.

5. A primer with an electric priming element comprising, a center electrode, a cylindrical outer electrode around said center electrode and extending axially beyond the latter, a primer pellet located in said axial extension of said outer electrode, a rim on said outer electrode bent towards said inner electrode and terminating in at least one contact point, an insulator provided between said center and outer electrodes and having a surface between said electrodes with a metallic coating thereon in connection with said electrodes, said primer having a shouldered bore therein with a metallic retaining ring therein, said outer electrode being mounted in said retaining ring, an anvil provided in said bore, and an insulating washer provided between said metallic retaining ring vand said anvil, said center electrode projecting through said insulating washer Iand being connected electrically with said anvil.

6. A primer -with an electric priming element comprising a center electrode, a cylindrical outer electrode around said center electrode and extending axially -beyond said center electrode, a primer pellet located in said axial extension of said outer electrode, a rim lon said outer electrode bent towards said inner electrode and terminating in `at least one contact point, an insulator provided between said center and outer electrodes and having a surface between said electrodes with -a metallic coating thereon in connection with said electrodes, said primer having `a shouldered bore therein, a metallic retaining ring in said bore and having said outer electrode mounted therein, an anvil provided in said bore, said anvil having an open-ended passageway therein, said center electrode being secured in said bore by solder, and an insulating washer provided between said metallic retaining ring and said anvil, said center electrode projecting through said insulating Washer.

References Cited by the Examiner UNITED STATES PATENTS FOREIGN PATENTS 12/ 1957 Germany. 10/ 1964 Germany.

BENJAMIN A. BORCHELT, Primary Examiner. 15 SAMUEL FEINBERG, Examiner.

R. V. LOTTMANN, V. R. PENDEGRASS,

Assistant Examiners. 

1. A PRIMER COMPRISING IN COMBINATION AN ELECTRIC PRIMING ELEMENT INCLUDING A CENTER ELECTRODE, A CYLINDRICAL OUTER ELECTRODE AROUND SAID CENTER ELECTRODE, A RIM ON SAID OUTER ELECTRODE BENT TOWARDS SAID CENTER ELECTRODE AND TERMINATING IN AT LEAST ONE CONTACT POINT, AN INSULATOR LOCATED BETWEEN SAID CENTER AND OUTER ELECTRODES AND HAVING A SURFACE BETWEEN SAID ELECTRODES, A METALLIC COATING ON SAID SURFACE IN CONNECTION WITH SAID ELECTRODES, MEANS FOR HOLDING SAID PRIMER ELEMENT INCLUDING A SLEEVELIKE BODY, SAID BODY HAVING AN OPEN-ENDED AXIAL BORE THERETHROUGH AND HAVING A FIRST END DIRECTED TOWARDS A MASS TO BE PRIMED BY THE PRIMER AND A SECOND END OPPOSITE TO SAID FIRST END DIRECTED OUTWARDLY FOR ELECTRICAL CONTACTING PURPOSES, AN INTERNAL SHOULDER AT SAID SECOND END, A METALLIC RETAINING RING IN SAID BORE, SAID PRIMER ELEMENT BEING MOUNTED IN ITS ENTIRETY IN SAID RETAINING RING BY FORCING IN SAID OUTER ELECTRODE, AN ANVIL LOCATED IN SAID BORE AND RESIDING ON SAID SHOULDER, A THIN INSULATING LAYER DISPOSED BETWEEN SAID SHOULDER AND SAID ANVIL, AN INSULATING WASHER DISPOSED BETWEEN SAID METALLIC RETAINING RING AND SAID ANVIL, SAID RETAINING RING BEING PRESSED IN A DIRECTION TO SAID SECOND END AGAINST SAID SHOULDER BY MEANS OF SAID INSULATING WASHER, SAID ANVIL AND SAID THIN INSULATING LAYER, AND SAID CENTER ELECTRODE OF SAID PRIMER ELEMENT PROJECTING THROUGH SAID INSULATING WASHER AND BEING CONNECTED ELECTRICALLY WITH SAID ANVIL. 